期刊
JOURNAL OF CELL SCIENCE
卷 120, 期 4, 页码 617-627出版社
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.03375
关键词
synaptotagmin; exocytosis; membrane fusion; Ca2+ sensor; dense-core vesicles
类别
资金
- NIDDK NIH HHS [DK25861, R01 DK025861, R37 DK025861] Funding Source: Medline
Synaptotagmin I is considered to be a Ca2+ sensor for fast vesicle exocytosis. Because Ca2+-dependent vesicle exocytosis persists in synaptotagmin I mutants, there must be additional Ca2+ sensors. Multiple synaptotagmin isoforms co-reside on vesicles, which suggests that other isoforms complement synaptotagmin I function. We found that full downregulation of synaptotagmins I and IX, which co-reside on vesicles in PC12 cells, completely abolished Ca2+-dependent vesicle exocytosis. By contrast, Ca2+-dependent exocytosis persisted in cells expressing only synaptotagmin I or only synaptotagmin IX, which indicated a redundancy in function for these isoforms. Although either isoform was sufficient to confer Ca2+ regulation on vesicle exocytosis, synaptotagmins I and IX conferred faster and slower release rates, respectively, indicating that individual isoforms impart distinct kinetic properties to vesicle exocytosis. The downregulation of synaptotagmin I but not synaptotagmin IX impaired compensatory vesicle endocytosis, which revealed a lack of isoform redundancy and functional specialization of synaptotagmin I for endocytic retrieval.
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